Substrate processing method and substrate processing apparatus

ABSTRACT

A substrate can be appropriately oxidized, while oxidation of the substrate can be suppressed. The present invention includes a step of generating mixed plasma by causing a mixed gas of hydrogen (H2) gas and oxygen(O2) or oxygen/containing gas supplied to a processing chamber to form a plasma discharge, and processing the starting substrate by the mixed plasma; and a step of generating hydrogen plasma by causing hydrogen (H2) gas supplied to the processing chamber to form a plasma discharge, and processing the substrate by the hydrogen plasma.

This application is a divisional of U.S. patent application Ser. No.11/886,529 now U.S. Pat. No. 8,066,994, filed Jan. 11, 2008, which is aNational Phase of Application No. PCT/JP2006/304960, filed Mar. 14,2006, which claims priority to Japanese Patent Application No.2005-075917, filed Mar. 16, 2005, and Japanese Patent Application No.2005-216666, filed July. 27, 2005, the entire contents of which arehereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a substrate processing method and asubstrate processing apparatus wherein a substrate is processed usingplasma.

BACKGROUND ART

A semiconductor device that has a multilayer wiring structure ismanufactured by repeatedly subjecting the surface of a silicon substrateor another such semiconductor wafer to film forming and pattern etching.For example, a floating gate layer, a control gate layer, and a controlgate electrode layer are layered on the silicon substrate from thebottom layer up in a device known as a flash memory, and this layeredfilm is patterned, thereby constructing a gate structure.

For the layered film, polysilicon, for example, is used for the floatinggate electrode layer, and tungsten (hereinafter W), for example, oranother such metal material and compounds thereof are used for thecontrol gate electrode layer. These films are typically formed by CVD(Chemical Vapor Deposition), sputtering, or another such method. Thefilm is patterned by using dry etching and physically shaving thesurface of the layered film.

However, as this gate structure is reduced in thickness and size, theleakage currents between the layers become impossible to ignore. It hasalso become impossible to ignore leakage currents from side walls thataccompany the miniaturization of the components. In the gate structureof a flash memory, the side wall portion is the most likely to haveleakage currents, and the edge portions in particular are likely to leakdue to electric field concentration. If the side walls are oxidized andthe leakage currents can be reduced, the properties of the componentsare improved, but conversely, when the control gate electrode that usesmetal elements is oxidized, the resistivity of the gate electrodeportion increases, and needle-shaped crystals known as whiskerspenetrate the adjacent film and grow, damaging the apparatus and leadingto an unavoidable loss in component properties and yield rate. Also, theexposed metal portion simultaneously sublimates in the atmosphere duringthe substrate processing and adheres to the processing container or thesubstrate, causing unacceptable metal contamination to occur.

These problems would be resolved if the W could be replaced with anoxidation-resistant material, but a suitable material has not yet beenfound. Therefore, another way to resolve these problems is to find amethod for oxidizing only the side walls of the polysilicon constitutingthe floating gate, without oxidizing the W used as the control gateelectrode. Specifically, there is a need for a selective oxidationtechnique that would be able to selectively oxidize the silicon alone.

In view of this, a method that has been considered in conventionalpractice as a selective oxidation process is a method for selectivelyoxidizing only the silicon by using plasma that is a mixture of hydrogengas and oxygen gas instead of moisture. An example of this conventionalselective oxidation method will be described using FIG. 7. After asubstrate has been conveyed into a processing chamber, the temperatureof the substrate is raised to a specific processing temperature(substrate temperature increase), and a mixed gas (H2+O2 gas) containinghydrogen gas (H2 gas) and oxygen gas (O2 gas) is fed into the processingchamber while the pressure in the processing chamber is adjusted to aspecific pressure (pressure adjustment). When the pressure in theprocessing chamber has stabilized, plasma discharge is initiated(discharge initiation), and the discharge is continued. This dischargecreates H2+O2 mixed plasma, and this mixed plasma selectively oxidizesthe side walls of the gate structure formed on the substrate surface(substrate processing).

The supply of mixed gas and the discharge are both stopped (dischargestopping), and the processing chamber is brought to the same pressure(approximately 100 Pa) as a vacuum transportation chamber (substrateconveying-out preparation) in order to convey the substrate from theprocessing chamber. Thus, an attempt is made to selectively oxidize onlythe silicon by using mixed plasma containing H2 gas and O2 gas.

As a relevant technique, in the step of creating the silicon oxide film,Ar is first introduced in order to prevent initial increased oxidationbecause Ar has the property of being easily discharged, and then oxygenis introduced and the oxygen radicals are activated (for example, seePatent Document 1). Another technique is to clean with hydrogen in orderto remove the naturally oxidized film (for example, see Patent Document2). Furthermore, another technique is to perform selective oxidation byreducing the tungsten (W) (for example, see Patent Document 3).

Patent Document 1: JP-A 2003-163213

Patent Document 2: JP-A 2000-150479

Patent Document 3: JP-A 8-102534

DISCLOSURE OF THE INVENTION Problems which the Invention is Intended toSolve

However, in conventional methods for oxidizing a substrate by using amixed gas of hydrogen and oxygen, hydrogen gas and oxygen gas aresupplied simultaneously to the processing chamber, and these mixed gasesare made to form a plasma discharge. Therefore, the oxygen gas israpidly excited and the substrate is rapidly oxidized, causing a problemwhereby the surface of the starting substrate becomes rough. Forexample, in cases in which the surface of the substrate is a metal, themetal is oxidized by the rapid excitation of the oxygen gas, and themetal surface sometimes becomes rough.

At the end of the oxidation process of the substrate by the mixed gas ofhydrogen gas and oxygen gas, when the supply of hydrogen gas and oxygengas is simultaneously halted to stop plasma discharge, it is clear thatcontamination has occurred and that the processing container has beencontaminated. For example, in cases in which the metal is exposed on thesubstrate, the metal is also oxidized in no small amount and theoxidized metal is sublimated, resulting in metal contamination.Therefore, after a certain number of substrates have been processed,contaminant matter adhering to the inside of the processing containermust be cleaned out, leading to the problem of reduced throughput.

An object of the present invention is to provide a substrate processingmethod and a substrate processing apparatus wherein a substrate can beoxidized to an appropriate degree, while the oxidation of the substratecan still be inhibited.

Another object of the present invention is to provide a substrateprocessing method and a substrate processing apparatus wherein oxidationof the substrate is inhibited and there is little surface roughness.

Yet another object of the present invention is to provide a substrateprocessing method and a substrate processing apparatus whereinthroughput can be improved by reducing the contamination that occurs atthe end of the substrate oxidation.

Means for Solving these Problems

The present invention provides a substrate processing method including astep of generating mixed plasma by causing a mixed gas of hydrogen gasand oxygen or oxygen-containing gas supplied to a processing chamber toform a plasma discharge, and processing the substrate by the mixedplasma; and a step of generating hydrogen plasma by causing hydrogen gassupplied to the processing chamber to form a plasma discharge, andprocessing the starting substrate by the hydrogen plasma.

Effects of the Invention

According to the present invention, in the step of processing with mixedplasma, the substrate can be oxidized to an appropriate degree becausethe substrate is processed by mixed plasma containing hydrogen gas andoxygen or oxygen-containing gas. In the step of processing with hydrogenplasma, oxidation of the substrate can be inhibited because thesubstrate is processed by hydrogen plasma.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiments of the present invention are described hereinbelow. Theplasma processing furnace of the present invention is a substrateprocessing furnace (hereinafter referred to as an MMT apparatus) forprocessing wafers and other such substrates with plasma by using amodified magnetron plasma source, which is capable of generatinghigh-density plasma with the aid of an electric field and a magneticfield. In this MMT apparatus, a substrate is placed in a processingchamber that is kept airtight, reaction gas is introduced into theprocessing chamber via a showerhead, the processing chamber is kept at aconstant pressure, high-frequency voltage is supplied to a dischargeelectrode to form an electric field and a magnetic field, and amagnetron discharge is induced. Electrons emitted from the dischargeelectrode continue circling in a cycloid movement while drifting toprovide longevity and an increased ionization rate, and high-densityplasma can therefore be created.

Thus, the reaction gas is excited and decomposed to subject thesubstrate surface to oxidization, nitridation, or another such diffusiontreatment; or to form a thin film on the substrate surface, to etch thesubstrate surface, or to subject the substrate to various other plasmaprocesses.

FIG. 6 shows a schematic structural diagram of this type of MMTapparatus. The MMT apparatus has a processing container 203, and thisprocessing container 203 is formed from a dome-shaped top container 210as a first container, and a bowl-shaped bottom container 211 as a secondcontainer, wherein the top container 210 covers the top of the bottomcontainer 211. The top container 210 is formed either from aluminumoxide or from quartz or another such non-metal material, and the bottomcontainer 211 is formed from aluminum. A susceptor 217, which is asubstrate holding tool (substrate holder) integrated with a heater,described later, is configured from aluminum or a non-metal materialsuch as ceramics, or quartz, thereby reducing the metal contaminantsthat penetrate into the film during processing.

A showerhead 236 is provided at the top of a processing chamber 201, andincludes a cap-shaped lid 233, a gas inlet port 234, a buffer chamber237, an opening 238, a shielding plate 240, and a gas blowing port 239.The buffer chamber 237 is provided as a dispersion space for dispersinggas introduced through the gas inlet port 234.

A gas supply tube 232 for supplying gas is connected to the gas inletport 234, and the gas supply tube 232 is joined to a gas cylinder ofreaction gas 230 (not shown) via a valve 243 a as an on-off valve, and amass flow controller 241 as a flow rate control device (flow ratecontroller). The reaction gas 230 is supplied from the showerhead 236 tothe processing chamber 201, and a gas exhaust port 235 is provided forexhausting gas to the side walls of the bottom container 211 so that thegas will flow from the periphery of the susceptor 217 towards the bottomof the processing chamber 201 after the substrate has been processed. Agas exhaust tube 231 for exhausting gas is connected to the gas exhaustport 235, and the gas exhaust tube 231 is connected to a vacuum pump246, which is an exhaust device, via an APC 242 as a pressure adjustingdevice and a valve 243 b as an on-off valve.

A cylindrical electrode 215, which is a first electrode formed in atubular shape, e.g., a cylindrical shape, is provided as a dischargemechanism (discharge part) for exciting the supplied reaction gas 230.The cylindrical electrode 215 is provided around the outer periphery ofthe processing container 203 (the top container 210) and encloses aplasma generating area 224 inside the processing chamber 201. Ahigh-frequency power source 273 is connected to the cylindricalelectrode 215, and this high-frequency power source applieshigh-frequency voltage via a matching box 272 for matching impedance.

Cylindrical magnets 216, which are magnetic field-forming mechanisms(magnetic field-forming part) formed in a tubular shape, e.g., acylindrical shape, act as cylindrical permanent magnets. The cylindricalmagnets 216 are disposed in the vicinity of the top and bottom ends ofthe outer surface of the cylindrical electrode 215. The upper and lowercylindrical magnets 216, 216 have magnetic poles at both ends (theinternal peripheral ends and the external peripheral ends) along theradial direction of the processing chamber 201, and the magnetic polesof the upper and lower cylindrical magnets 216, 216 are inverselypolarized. Therefore, the magnetic poles on the internal periphery areheteropolar, thereby forming a line of magnetic force in the axialdirection of the cylinder along the internal peripheral surface of thecylindrical electrode 215.

A susceptor 217 as a substrate holding tool (substrate holding mean) forholding a wafer 200 as a substrate is disposed in the center of thebottom of the processing chamber 201. The susceptor 217 is formed from,e.g., aluminum nitride or a non-metal material such as ceramics orquartz, and a heater (not shown) as a heating mechanism (heater) isintegrally embedded in the interior, making it possible to heat thewafer 200. The heater can heat the wafer 200 to a temperature of 700 to800° C. when supplied with electric power.

A second electrode as an electrode for varying the impedance is alsoinstalled in the susceptor 217, and this second electrode is groundedvia an impedance variation mechanism 274. The impedance variationmechanism 274 is configured from a coil or a variable capacitor, and theelectric potential of the wafer 200 can be controlled via theaforementioned electrodes and the susceptor 217 by controlling thenumber of coil patterns or the capacitance value of the variablecapacitor.

A processing furnace 202, which is used to process the wafer 200 bymagnetron discharge in the magnetron plasma source, is configured atleast from the processing chamber 201, the processing container 203, thesusceptor 217, the cylindrical electrode 215, the cylindrical magnets216, the showerhead 236, and the gas exhaust port 235; and allows thewafer 200 to be processed with a plasma in the processing chamber 201.

A shielding plate 223 is provided around the periphery of thecylindrical electrode 215 and the cylindrical magnets 216 to effectivelyshield the electric field and the magnetic field, so that the electricfield and magnetic field formed by the cylindrical electrode 215 and thecylindrical magnets 216 do not adversely affect the externalenvironment, other processing furnaces, or other such devices.

The susceptor 217 is insulated from the bottom container 211, and isprovided with a susceptor elevating/lowering mechanism(elevating/lowering part) 268 for raising and lowering the susceptor217. Through-holes 217 a are also provided in the susceptor 217, andwafer upthrust pins 266 for thrusting up the wafer 200 are provided inat least three locations in the bottom surface of the bottom container211. The through-holes 217 a and the wafer upthrust pins 266 aredisposed so as to have a positional relationship in which the waferupthrust pins 266 pass through the through-holes 217 a without cominginto contact with the susceptor 217 when the susceptorelevating/lowering mechanism 268 lowers the susceptor 217.

A gate valve 244 that acts as a sluice valve is provided in the sidewall of the bottom container 211. When this valve is open, the wafer 200can be conveyed into or out of the processing chamber 201 by a conveyingmechanism (conveyor) (not shown), and when the valve is closed, theprocessing chamber 201 can be hermetically sealed.

A controller 121 as controller is configured to control the APC 242, thevalve 243 b, and the vacuum pump 246 through a signal wire A; to controlthe susceptor elevating/lowering mechanism 268 through a signal wire B;to control the gate valve 244 through a signal wire C; to control anintegrator 272 and the high-frequency power source 273 through a signalwire D; to control the mass flow controller 241 and the valve 243 athrough a signal wire E; and to control the impedance variationmechanism 274 and the heater embedded in the susceptor through anothersignal wire (not shown).

Next, the substrate processing method of Embodiment 1 will be describedusing the gas flow and discharge sequence shown in FIG. 1. Thissubstrate processing method uses a processing furnace having aconfiguration such as the one described above, wherein the step ofmanufacturing a semiconductor device is one step, and specific plasmaprocessing is performed on the wafer 200 surface, or on the surface of abase film formed on the wafer 200.

Following is a description of a case of selectively oxidizing a wafersurface (device surface) having a configuration in which a polysiliconfilm and a metal film, e.g., tungsten (W), are exposed. This type ofconfiguration is typified by a gate structure of a flash device. Thegate structure of a flash device is created, for example, bysequentially layering over a silicon substrate a tunnel gate oxide film,a floating electrode composed of a polysilicon layer, aninterpolysilicon layer having an ONO (oxide film-nitride film-oxidefilm) structure, and a control electrode composed of a two-layerstructure that has a polysilicon layer and a W layer.

In the following description, the controller 121 controls the operationsof the components constituting the substrate processing apparatus.

Substrate Conveying-in Step

The wafer 200 is conveyed into the processing chamber 201 by a conveyingmechanism (not shown) for conveying wafers from the exterior of theprocessing chamber 201 constituting the processing furnace 202, and thewafer is placed on the susceptor 217. The details of this conveyingoperation are as follows. The susceptor 217 is lowered to a substrateconveying position, and the distal ends of the wafer upthrust pins 266pass through the through-holes 217 a in the susceptor 217. At this time,the wafer upthrust pins 266 protrude upward a specific height from thesurface of the susceptor 217.

Next, the gate valve 244 provided to the bottom container 211 opens, andthe conveying mechanism (not shown) places the wafer 200 on the distalends of the wafer upthrust pins 266. When the conveying mechanismretracts to the outside of the processing chamber 201, the gate valve244 closes. When the susceptor 217 is raised by the susceptorelevating/lowering mechanism 268, the wafer 200 can be placed on the topsurface of the susceptor 217, and the wafer 200 can be raised to aposition for processing.

Step of Raising Substrate Temperature

The heater embedded in the susceptor 217 is heated in advance, and theconveyed-in wafer 200 is heated to a specific wafer processingtemperature that ranges from room temperature to 700° C. The vacuum pump246 and the APC 242 are used to keep the pressure of the processingchamber 201 at a specific level within a range of 0.1 to 266 Pa.

Pressure Adjustment Step (Hydrogen (H₂) Gas Preliminary IntroductionStep)

Once the wafer 200 has been heated to the processing temperature,hydrogen is supplied by introducing H₂ gas from the gas inlet port 234via the gas blowing port 239 of the shielding plate 240, and the gas isintroduced in the form of a shower onto the surface (processing surface)of the wafer 200 disposed in the processing chamber 201 (H₂ gaspreliminary introduction step). At this time, the amount of H₂ gas flowis in the range of 100 to 1000 sccm. The vacuum pump 246 and the APC 242are used to adjust the atmospheric pressure in the processing chamber201 to a range of 0.1 to 266 Pa.

The reason the lower limit of the range of the H₂ gas flow rate is 100sccm is because this flow rate is necessary for pressure adjustment. Thereason the upper limit of the H₂ gas flow rate is 1000 sccm is becausethis is the limit of the supply conduit, and a greater gas flow rate maybe used if possible. The reason the lower limit of the pressure range is0.1 Pa is because this is the lower limit of low-pressure control. Thereason the upper limit of the pressure range is 266 Pa is because if thepressure is any higher, the rate of film formation is reduced, which isundesirable.

The H₂ gas supplied in the pressure adjustment step is suppliedcontinuously in a first step, a second step, a third step, and a fourthstep, which are described later.

Hydrogen Plasma Discharge Step (First Step)

When the pressure in the processing chamber 201 has stabilized,high-frequency voltage is applied to the cylindrical electrode 215 fromthe high-frequency power source 273 via the integrator 272 to induce aplasma discharge, and this discharge is continued (discharge after theinitiation of discharge). The applied high-frequency voltage has anoutput value within a range of about 100 to 500 W. At this time, theimpedance variation mechanism 274 is controlled in advance to a desiredimpedance value. Since the atmosphere in the processing chamber 201contains only H₂, the application of high-frequency voltage causeshydrogen plasma to be generated in the processing chamber 201. Thehydrogen plasma contains H⁺ (hydrogen ions), H* (hydrogen radicals), andthe like. Since the H⁺ and H* create a reducing atmosphere, thisatmosphere suppresses the oxidation of the W surface exposed on thewafer 200.

It is believed that oxygen gas (O₂ gas) remains in the gas of the firststep as a result of the preliminary wafer processing, but it is alsobelieved that the amount is not sufficient to cause roughness in the Wsurface. The oxygen concentration is enough to sufficiently suppressoxidation if the processing container is evacuated for about 30 seconds,for example, and is preferably 12% or less. Particularly, theoxygen/hydrogen ratio is preferably 8:1, and the hydrogen concentrationis preferably 11.1%.

Plasma discharge is performed continuously in the second step, whichfollows the first step.

Substrate Processing Step (Second Step)

After a specific amount of time, e.g., 3 to 5 seconds, or preferablyabout 5 seconds, has passed since the start of plasma discharge, O₂ gasbegins to be introduced from the gas inlet port 234 via the gas blowingport 239 of the shielding plate 240, and the gas flow contains a mixedgas of H₂ gas and O₂ gas. The aforementioned specific time should beshort because of considerations related to throughput, but a time ofabout 3 to 5 seconds is necessary until the plasma discharge can bestably controlled.

The introduction of O₂ gas into the processing chamber 201 is designedto ensure that the plasma discharge gradually adds O₂ to the H₂ gasatmosphere. In FIG. 1, the border between the preliminary H₂ gas and thefollowing (H₂+O₂) gas is indicated as a slant. The reason O₂ gas isgradually added herein is to prevent more rapid plasma excitation of theO₂ due to discharge, and to more reliably prevent rapid oxidation fromoccurring on the surface of the wafer.

In the MMT apparatus of this embodiment, the H₂ gas and O₂ gas are mixedinside the gas supply tube 232, and are controlled so that the flowratio of O₂:H₂ is ultimately about 1:8. The reason that the O₂:H₂ flowratio is rich in hydrogen at 1:9 is because if the flow ratio is anyhigher (if the percentage of O₂ is any greater), selective oxidationbetween the W and the polysilicon is no longer possible.

It is generally preferable for the H₂ percentage to increase becausereduction increases accordingly and oxidation of the W surface isfurther suppressed, but it is also not preferable because the oxidationrate of the polysilicon surface is conversely reduced. Therefore, if thereduction in the oxidation rate is within an acceptable range, the flowratio is preferably less than 1:8 (the H₂ percentage is increased).

However, an MMT apparatus in particular has the superior characteristicsin that the oxidation rate is not reduced even when the O₂:H₂ flow ratiois reduced (even when the percentage of H₂ is increased), in contrast toa common plasma apparatus. The MMT apparatus is therefore suitable asthe oxidation processing apparatus of the present invention.

As a result of introducing O₂ gas into the processing chamber 201,high-density plasma of a mixed gas (H₂+O₂ gas) of H₂ gas and O₂ gas isgenerated in the plasma generating area 224. As a result of thegenerated high-density plasma, plasma processing is performed on thesurface of the wafer 200 on the susceptor 217. At this time, the mixedgas of H₂ gas and O₂ gas is separated by the plasma, creating H, OH, andthe like. The OH acts on the silicon and the W to oxidize both films.The H is reducing in relation to W and therefore effectively reduces theoxidized W surface, but also has little reducing strength in relation topolysilicon. The polysilicon is therefore oxidized as a result, but theW surface is not oxidized.

In Embodiment 1 as described above, the following are the reasons forproviding a first step to introduce H₂ gas in advance instead ofintroducing H₂ gas and O₂ gas simultaneously in the second step.

The reducing strength of H₂ is less than the oxidation strength of O₂,and the W is oxidized and the surface of the W becomes rough in cases inwhich the gases are introduced simultaneously. The result of thisroughening is that the wafer surface becomes uneven and the sheathresistance is not constant. Tungsten oxide is produced by the oxidationof the W surface, and this tungsten oxide adheres to the processingcontainer 203 and the wafer. This adhesion on the processing container203 affects the following wafer processing, the adhesion on the wafer200 causes problems such as deterioration of the tunnel gate oxide film,and a leak current is generated as a result. In view of this, the amountof H₂ gas introduced in advance in the first step is kept sufficient forreduction, and O₂ gas is introduced in the second step while H₂ gascontinues to be introduced.

In this case, the flow ratio of O₂ gas in relation to H₂ gas in thefirst step is preferably less than the flow ratio of O₂ gas in relationto H₂ gas in the second step. Furthermore, it is preferable that H₂ gasbe supplied in the first step and that that H₂ gas continue to besupplied in the second step while oxygen O₂ is supplied in addition toH₂ gas. Furthermore, the flow rate of O₂ gas contained in the gas in thefirst step is preferably less than the flow rate of O₂ gas contained inthe mixed gas in the second step. Furthermore, it is more preferablethat no O₂ gas be supplied in the first step.

The gas introduced in the first step and second step may be any reducinggas that does not react with silicon. Ammonia is an example of areducing gas, but cannot be used in selective oxidation because ammoniabrings about nitridation. In cases in which Ar is introduced as in theprior art documents, the Ar activates oxidation, and is therefore notsuitable for the selective oxidation of the present invention.

Step of Preparing Substrate to be Conveyed Out

After the supply of H₂+O₂ gas and discharge are stopped for theselective oxidation process, the interior of the processing chamber 201is brought to the same pressure as the adjacent vacuous conveyingchamber in order to convey the processed wafer 200 out of the processingchamber 201.

Substrate Conveying-Out Preparation Step

After the oxidation process is ended, the conveyor (not shown) is usedto convey the wafer 200 to a specific position outside of the processingchamber 201 in the opposite sequence from the substrate introductionstep, and the wafer 200 is cooled to a specific temperature andwithdrawn outside of the apparatus.

The series of steps described above is performed, thus completing thewafer oxidation process.

In this series of steps, control is performed over the electric powercontrol of the high-frequency power source 273 by the controller 121,adjustment of the integrator 272, the opening and closing of the valve243 a, the flow rate of the mass flow controller 241, the degree ofopening of the APC 242, the opening and closing of the valve 243 b, thestarting and stopping of the vacuum pump 246, the raising and loweringoperation of the susceptor elevating/lowering mechanism 268, the openingand closing of the gate valve 244, and the electric power control to thepower source for applying voltage to the heater embedded in thesusceptor.

According to Embodiment 1 described above, since O₂ gas and H₂ gas aresupplied to the wafer in which the W film and polysilicon film areexposed in the device surface, the oxidation of the device surface canbe suppressed. The oxidation of the W surface exposed on the wafer 200is suppressed also because plasma discharge is performed to generatehydrogen plasma after a specific amount of time has passed since thesupply of H₂ gas was begun, and the wafer is left in a hydrogen plasmaatmosphere as a reducing atmosphere. Reduction can be maintained becauseH₂ gas continues to flow into the processing chamber in which plasmadischarge continues. Since the atmosphere over the waver does notcontain O₂ at the start of plasma discharge, the wafer is not oxidizedrapidly, and it is possible perform a selective oxidation process thatdoes not cause W surface roughness.

Rapid excitation of the O₂ gas can be inhibited, as can rapid oxidationof the wafer, because discharge is initiated in an H₂ gas atmosphere andO₂ gas is then gradually added, whereby appropriate oxidation can becontinued while maintaining reduction. Oxidation of the W portionexposed on the wafer can be more reliably suppressed, and it is possibleto more reliably oxidize only the polysilicon layer because the mixedgas of H₂ gas and O₂ gas is caused to form a plasma discharge togenerate OH, H, and the like.

When the interior of the processing chamber is purged by H₂ gas afterthe pressure adjustment step preceding discharge initiation forgenerating H₂ plasma, the O₂ concentration in the processing chamber canbe reduced, and more efficient selective oxidation can be performed.Furthermore, oxidation of the wafer from the temperature-raising stageonward can be suppressed by raising the temperature while feeding H₂ gasalso during the substrate temperature-raising step preceding thepressure adjustment step.

Particularly, when a MMT (modified magnetron) system is used as theplasma generating method for exciting O₂ and H₂ mixed gas or H₂ gasonly, the structure can be simplified because existing facilities can beused without modification. Using plasma makes it possible to selectivelyoxidize a wafer at a low temperature of 700° C. or less. Oxidation ofthe W layer can be reliably prevented because the flow ratio of O₂:H₂can be reduced without reducing the oxidation rate.

As shown in FIG. 1, an experiment for oxidizing the surface of the Wsubstrate was conducted in order to evaluate the process when H₂ gas isfed in the first step to reduce the wafer, and H₂ gas and O₂ gas are fedin the second step and simultaneously stopped to selectively oxidize thewafer.

FIG. 2 is an SEM photograph showing the experiment results obtained whenthe oxidation process is performed on the surface of a W substrate. (a)shows an unprocessed surface, (b) shows a surface oxidized in an O₂atmosphere (Comparative Example 1), (c) shows a surface oxidized in anO₂+H₂ atmosphere (Comparative Example 2), and (d) shows a surfaceoxidized by adding O₂ while performing the process in the H₂ atmosphereof the example (Example).

The common oxidation conditions are a heater set temperature of 900° C.,a furnace internal pressure of 100 Pa, and an applied voltage of 350 W.The O₂ flow rate in Comparative Example 1 is 400 sccm, and the O₂ gasflow rate is 44 sccm while the H₂ gas flow rate is 356 sccm (flow ratioof O₂ gas and H₂ gas is 1:8) in Comparative Example 2 and in the Example

It is clear from FIG. 2 that in the Example (d), the W substrate surfacewas not oxidized and there was no surface roughness, while inComparative Example 1 (b), the surface was oxidized, and surfaceroughness occurred to the extent that the surface shape changed andcrystal grains of tungsten oxide could be confirmed. In ComparativeExample 2(c), the surface was slightly oxidized and surface roughnessremained. Therefore, it was thereby made clear that the method of theoxidation process in the present Example was effective for suppressing Woxidation and that this method made it possible to prevent W surfaceroughness.

Therefore, if the oxidation processing method of the present inventionis applied to the oxidation step in a gate structure of a flash memorythat uses W or another such metal in a control gate electrode, forexample, the control gate electrode portion exposed on the substrate isnot oxidized, and side walls of the polysilicon portion can beeffectively oxidized.

However, in selective oxidation, it is clear that when the O₂ gas and H₂gas are simultaneously stopped, W is generated, and the surface iscontaminated by the W. Several causes for this have been considered, andalthough it is not clearly understood, it is believed that the oxygenplasma knocks out contaminant substances from the wafer, theseknocked-out contaminant substances are suspended within the plasma, andthe substances adhere to the interior of the processing chamber when theplasma discharge is stopped. Therefore, the W adhering to the interiorof the processing container 203 must be cleaned out after a specificnumber of wafers have been processed, and throughput is reduced. Toresolve this problem, the suspended amount of W must be reduced beforeplasma discharge is stopped.

FIG. 3 is a diagram of the gas flow and discharge sequence, wherein thesubstrate processing method of Embodiment 2 is described. The differencefrom Embodiment 1 shown in FIG. 1 is that in Embodiment 1, the supply ofH₂ gas and O₂ gas was simultaneously stopped to stop plasma dischargewhen selective oxidation by mixed plasma had ended, while in Embodiment2, the supply of H₂ gas is continued for a certain time after the supplyof O₂ gas is stopped, and the wafer continues to be processed byhydrogen plasma.

In the Embodiment 2 described hereinbelow, the substrate processing stepis referred to as the third step despite being identical to the firstsubstrate processing step (the second step). The reason for this isbecause a fourth step performed after the third step of Embodiment 2does not necessarily need to be added as a continuation of the thirdstep after the hydrogen plasma discharge step (first step) and thesubstrate processing step (second step) of Embodiment 1, and an O₂ gasintroduction stopping step may be performed after the substrateprocessing step, separate from the hydrogen plasma discharge step.Therefore, the substrate processing step identical to that of Embodiment1 is referred to as a third step.

Substrate Processing Step (Third Step)

As shown in FIG. 3, the wafer 200 is subjected to a selective oxidationprocess by mixed plasma containing H₂ gas and O₂ gas, similar to thesubstrate processing step (second step) of Embodiment 1.

O₂ Gas Introduction Stopping Step (Fourth Step)

As plasma discharge for the selective oxidation process is about to end,the oxygen flow is stopped, H₂ gas alone is used for the gas flow, andan electric discharge is performed in which the high-frequency voltageapplied from the high-frequency power source 273 is reduced to about 100W or less, which is lower than the third step. The reduction indischarge electric power is shown in FIG. 3 by the gradual reduction inthe height indicating the discharged amount. As a result of using onlyH₂ gas for the gas flow and reducing the electric power of the dischargeto about 100 W, only the H in the atmosphere in the processing chamber201 is excited, and the W in the atmosphere in the processing chamber201 is reduced by the excited H and is quickly exhausted out of theprocessing chamber 201. The applied high-frequency voltage may bereduced incrementally or continuously.

The valve 243 a is closed to stop the supply of H₂ gas from the gasinlet port 234, the application of high-frequency voltage to thecylindrical electrode 215 is stopped to end the substrate processing,and preparations to convey out the substrate are begun.

The reason that the generation of W can be inhibited by stopping theinflow of O₂ gas is not necessarily clear, but is estimated to be asfollows.

Since oxygen radicals have greater longevity than hydrogen radicals, itis believed that the oxygen radicals remain longer than the hydrogenradicals in cases in which the inflows of H₂ gas and O₂ gas are stoppedsimultaneously. As a result, the W is oxidized by the remaining oxygenradicals and is scattered throughout the processing container 203. Inview of this, stopping first the inflow of O₂ gas results in thelongevity of the hydrogen radicals and oxygen radicals expiringsimultaneously so that no O₂ gas remains and the generation of W issuppressed.

In this case, the oxygen concentration in the gas in the fourth step isenough to sufficiently suppress oxidation if the processing container isevacuated for about 30 seconds, for example, and is preferably 12% orless. Particularly, the oxygen/hydrogen ratio is preferably 1:8, and thehydrogen concentration is preferably 11.1%. The flow ratio of O₂ gas inrelation to H₂ gas in the fourth step is preferably less than the flowratio of O₂ gas in relation to H₂ gas in the third step. Furthermore, itis preferable that the wafer be selectively oxidized by the mixed plasmain the third step, and that the supply of O₂ gas be stopped in thefourth step. Furthermore, the flow rate of O₂ gas contained in the gasin the fourth step is preferably less than the flow rate of O₂ gascontained in the mixed gas in the third step. Furthermore, O₂ gas ispreferably not supplied in the fourth step.

Thus, in Embodiment 2, the oxygen plasma and the hydrogen plasma performselective oxidation in the third step, the supply of O₂ gas is stoppedin the fourth step, H₂ gas plasma alone is generated, and contaminationwith W from the wafer 200 is suppressed. The amount of suspended W priorto the stopping of plasma discharge can thereby be reduced, and eitherno or very little, if any, W oxide therefore adheres to the interior ofthe processing container 203 even after the same number of wafers as inthe conventional example are processed. Therefore, there is no need toclean the W, and throughput can be further improved.

As shown in FIG. 3, experiments were conducted regarding conditionsunder which metal contamination occurred in processing containers 203 towhich the gas flows and discharge sequences of Embodiment 2 (FIG. 3) andthe conventional example (FIG. 7) were respectively applied. The aim ofthe experiments was to evaluate the process in which selective oxidationwas performed by the oxygen plasma and hydrogen plasma in the thirdstep, the supply of O₂ gas was stopped in the fourth step, H₂ gas plasmaalone was generated, and contamination with W from the wafer wassuppressed.

FIGS. 4 and 5 show the results of experiments regarding conditions underwhich metal contamination occurred in the processing containers 203 inwhich Embodiment 3 and the conventional example were respectivelyapplied. The vertical axis shows concentration in units of atms/cm². Thehorizontal axis shows the elements Li, Na, Mg, Al, K, Ca, Cr, Mn, Fe,Ni, Cu, Zn, and particularly W, aligned from left to right. Thecontamination concentration of each metal is shown in a bar graph.

In FIG. 4, the terms “before processing,” “After 10,” “After 25,” andthe like refer to the contamination conditions before the first wafer isprocessed, the contamination conditions after the tenth wafer isprocessed, the contamination conditions after the twenty-fifth wafer isprocessed, and the like. In FIG. 5, the terms “After one,” “After 10,”and the like similarly refer to the contamination conditions after thefirst wafer is processed, the contamination conditions after the tenthwafer is processed, and the like. The bar graphs showing thecontamination conditions are drawn so that when multiple bars arealigned adjacently for the same metal, the number of wafers processedincreases from left to right.

In the W contamination conditions in the conventional example shown inFIG. 5, high W concentrations were detected, wherein the concentrationhad already reached nearly 1.70×10¹¹ [atms/cm²] after the “first,” andthe concentration exceeded 1.00×10¹² [atms/cm²] from the “second” to“after ten.”

In the W contamination conditions in the Embodiment shown in FIG. 4, alow W concentration of about 1.3×10¹⁰ [atms/cm²] is shown even afterfive and ten wafers, and it is clear that the W concentration issignificantly reduced in comparison with the conventional example. The Wconcentration does not increase from 15 wafers onward and never exceeds1.50×10¹⁰ [atms/cm²], and it is therefore clear that metal contaminationby W can be continuously reduced.

A case was described in which the substrate processing methods ofEmbodiments 1 and 2 described above were performed separately andindependently, but the present invention is not limited to this optionalone. The substrate processing step (second step) of Embodiment 1 andthe substrate processing step (third step) of Embodiment 2 can betreated as the same step, and the first through fourth steps can beperformed as one continuous step, in which case the effects ofpreventing surface roughness and W contamination are particularlygreater.

In the embodiments described above, O₂ gas was used in a mixed gas withH₂ gas, but an oxygen-containing gas other than O₂ may be used, andexamples of oxygen-containing gases include nitrous oxide (N₂O) gas andnitric oxide (NO) gas. In addition to tungsten (W), examples of themetal to which the present invention can be applied include Mo(molybdenum), Pa (palladium), Ro (Rhodium), Ru (rubidium), Ni (nickel),Co (cobalt), Ta (tantalum), Ti (titanium), Al (aluminum), Cu (copper),and the like. A case was described in the embodiments in which thepresent invention was applied to the gate structure of a flash memory,but the present invention can also be applied to the gate structure of aDRAM.

The preferred aspects of the present invention are described.

A first aspect is a substrate processing method including a step ofgenerating mixed plasma by causing a mixed gas of hydrogen gas andoxygen or oxygen-containing gas supplied to a processing chamber to forma plasma discharge, and processing the substrate by the mixed plasma;and a step of generating hydrogen plasma by causing hydrogen gassupplied to the processing chamber to form a plasma discharge, andprocessing the substrate by the hydrogen plasma.

In the step of performing the process with mixed plasma, the substrateis processed with mixed plasma containing hydrogen gas and oxygen oroxygen-containing gas, and the substrate can therefore be appropriatelyoxidized. In the step of performing the process with hydrogen plasma,the substrate is processed with hydrogen plasma, and oxidation of thesubstrate can therefore be suppressed.

A second aspect is the first aspect, wherein the step of performing aprocess with the hydrogen plasma is a first step, and a step ofperforming a process with the mixed plasma is performed as a second stepafter the first step.

When hydrogen gas and oxygen gas are supplied simultaneously, it isbelieved that a phenomenon occurs in which only the oxygen is firstactivated immediately after the plasma discharge begins, the surface ofthe substrate is slightly oxidized, the subsequent activation ofhydrogen causes the oxide film to be removed, and surface roughnessremains in the substrate. Therefore, a first step of performing plasmadischarge with only hydrogen gas is first carried out, a second step isthen performed in which hydrogen gas and oxygen gas are both supplied,and an oxidation process is begun, as in the present aspect. When thesesteps are performed, the substrate can be oxidized while suppressing theoxidation of the substrate, and a process can be performed to suppressrapid oxidation of the substrate, resulting in little surface roughness.

A third aspect is the second aspect, wherein the oxygen concentration inthe gas in the first step is 1 part oxygen per 8 parts hydrogen byvolume (11.1% or less).

In cases in which oxygen remains on the substrate during the first step,a problem is particularly likely to be encountered in which reduction ofsubstrate oxidation is insufficient. According to the present aspect,however, oxidation of the substrate can be reliably suppressed, and aprocess resulting in less surface roughness can be performed since theoxygen concentration is 11.1% or less.

A fourth aspect is the second aspect, wherein the flow ratio of oxygengas in relation to the hydrogen gas in the first step is less than theflow ratio of oxygen gas in relation to the hydrogen gas in the secondstep.

In cases in which the gas contains oxygen gas during the first step, aproblem is particularly likely to be encountered in which oxidation ofthe substrate is inadequately suppressed. According to the presentaspect, however, oxidation of the substrate can be reliably suppressedbecause the oxygen gas flow ratio in the first step is less than theoxygen gas flow ratio in the second step. In the second step, since theoxygen gas flow ratio in the second step is greater than the oxygen gasflow ratio in the first step, the substrate can be appropriatelyoxidized, and a process resulting in less surface roughness can beperformed.

A fifth aspect is the second aspect, wherein hydrogen gas is supplied inthe first step, and the supply of the hydrogen gas is continued whileoxygen gas is supplied in addition to the hydrogen gas in the secondstep.

In cases in which oxygen remains on the substrate during the first step,in which oxidation of the substrate is inadequately suppressed.According to the present aspect, however, hydrogen gas is supplied inthe first step, and oxidation of the substrate can therefore be reliablysuppressed. In the second step, since oxygen gas is supplied in additionto hydrogen gas, the substrate can be appropriately oxidized, and aprocess resulting in less surface roughness can be performed.

A sixth aspect is the second aspect, wherein the flow rate of oxygen gascontained in the gas in the first step is less than the flow rate ofoxygen gas contained in the mixed gas in the second step.

In cases in which the gas contains oxygen gas during the first step, aproblem is particularly likely to be encountered in which the reductionof substrate oxidation is insufficient. According to the present aspect,however, oxidation of the substrate can be reliably suppressed becausethe oxygen gas flow rate in the first step is less than the oxygen gasflow rate in the second step. In the second step, since the oxygen gasflow rate in the second step is greater than the oxygen gas flow rate inthe first step, the substrate can be appropriately oxidized, and aprocess resulting in less surface roughness can be performed.

A seventh aspect is the second aspect, wherein oxygen gas is notsupplied in the first step.

In cases in which oxygen gas is supplied during the first step, aproblem is particularly likely to be encountered in which oxidation ofthe substrate is inadequately suppressed. According to the presentaspect, however, oxidation of the substrate can be reliably suppressed,and a process resulting in less surface roughness can be performed sinceoxygen gas is not supplied in the first step.

An eighth aspect is the first aspect, wherein a step of performing aprocess with the mixed plasma is a third step, and a step of performinga process with the hydrogen plasma is performed as a fourth step afterthe third step.

It is believed that the oxygen plasma knocks out contaminant substancesfrom the substrate, that these knocked-out contaminant substances aresuspended in the plasma, and that the substances adhere to the substratewhen the plasma discharge is stopped. Therefore, when a fourth step isperformed in which the process is carried out with hydrogen plasma afterthe third step as in the present aspect, contamination occurring at theend of oxidation can be reduced to improve throughput.

A ninth aspect is the eighth aspect, wherein the oxygen concentration inthe gas in the fourth step is enough to sufficiently suppress oxidationif the processing container is evacuated for about 30 seconds, and ispreferably 12% or less. Particularly, the oxygen/hydrogen ratio ispreferably 8:1, and the oxygen concentration is preferably 11.1%.

In cases in which oxygen remains during the fourth step, contaminationby the oxygen is particularly likely to be a problem. According to thepresent aspect, however, contamination occurring at the end of oxidationcan be reliably reduced to improve throughput since the oxygenconcentration is 11.1%.

A tenth aspect is the eighth aspect, wherein the flow ratio of oxygengas in relation to the hydrogen gas in the third step is less than theflow ratio of oxygen gas in relation to the mixed gas in the fourthstep.

In cases in which the gas contains oxygen gas during the fourth step, aproblem of insufficiently reduced contamination is particularly likelyto be encountered. According to the present aspect, however,contamination occurring at the end of oxidation can be reliably reducedto improve throughput since the flow ratio of oxygen gas in the fourthstep is less than the flow ratio of oxygen gas in the third step.

An eleventh aspect is the eighth aspect, wherein the substrate isselectively oxidized by the mixed plasma in the third step, and thesupply of oxygen gas is stopped in the fourth step.

In cases in which the gas contains oxygen gas during the fourth step, aproblem of insufficiently reduced contamination is particularly likelyto be encountered. According to the present aspect, however,contamination occurring at the end of oxidation can be reliably reducedto improve throughput since the supply of oxygen gas is stopped in thefourth step.

A twelfth aspect is the eighth aspect, wherein the flow rate of oxygengas contained in the gas in the fourth step is less than the flow rateof oxygen gas contained in the mixed gas in the third step.

In cases in which the gas contains oxygen gas during the fourth step, aproblem of insufficiently reduced contamination is particularly likelyto be encountered. According to the present aspect, however,contamination occurring at the end of oxidation can be reliably reducedto improve throughput since the flow rate of oxygen gas in the fourthstep is less than the flow rate of oxygen gas in the third step.

A thirteenth aspect is the eighth aspect, wherein oxygen gas is notsupplied in the fourth step.

In cases in which the gas contains oxygen gas during the fourth step, aproblem of insufficiently reduced contamination is particularly likelyto be encountered. According to the present aspect, however,contamination occurring at the end of oxidation can be reliably reducedto improve throughput since oxygen gas is not supplied in the fourthstep.

A fourteenth aspect includes a processing chamber that processes asubstrate; a mixed gas inlet port that introduces a mixed gas ofhydrogen gas and oxygen or oxygen-containing gas into the processingchamber; a hydrogen gas inlet port that introduces hydrogen gas into theprocessing chamber; an exhaust port that evacuates the interior of theprocessing chamber; plasma generating part that generates mixed plasmaby causing the mixed gas introduced into the processing chamber to forma plasma discharge, and generates hydrogen plasma by causing thehydrogen gas introduced into the processing chamber to form a plasmadischarge; and controller that performs control so that the mixed gasintroduced through the mixed gas inlet port is caused to form a plasmadischarge and is supplied to the processing chamber while exhaustedthrough the exhaust port, and so that the hydrogen gas introducedthrough the hydrogen gas inlet port is caused to form a plasma dischargeand is supplied to the processing chamber while exhausted through theexhaust port.

The substrate processing method of the first aspect can easily beimplemented by providing controller that performs control so that mixedplasma introduced through the mixed gas supply port and generated byplasma discharge is supplied to the processing chamber while exhaustedout through the exhaust port, and hydrogen plasma introduced through thehydrogen gas supply port and generated by plasma discharge is suppliedto the processing chamber while exhausted out through the exhaust port.

A fifteenth aspect is the fourteenth aspect, wherein the controllerperforms control so that the hydrogen gas introduced through thehydrogen gas inlet port is caused to form a plasma discharge andsupplied to the processing chamber while exhausted through the exhaustport, and thereafter the mixed gas introduced through the mixed gasinlet port is caused to form a plasma discharge and supplied to theprocessing chamber while exhausted through the exhaust port.

The substrate processing method of the second aspect can be easilyimplemented when the controller performs control so that hydrogen plasmaintroduced through the hydrogen gas supply port and generated by plasmadischarge is supplied to the processing chamber while exhausted outthrough the exhaust port, and mixed plasma introduced through the mixedgas supply port and generated by plasma discharge is supplied to theprocessing chamber while exhausted out through the exhaust port.

A sixteenth aspect is the fourteenth aspect, wherein the controllerperforms control so that the mixed gas introduced through the mixed gasinlet port is caused to form a plasma discharge and supplied to theprocessing chamber while exhausted through the exhaust port, andthereafter the hydrogen gas introduced through the hydrogen gas inletport is caused to form a plasma discharge and supplied to the processingchamber while exhausted through the exhaust port.

The substrate processing method of the eighth aspect can be easilyimplemented when the controller performs control so that mixed plasmaintroduced through the mixed gas supply port and generated by plasmadischarge is supplied to the processing chamber while exhausted outthrough the exhaust port, and hydrogen plasma introduced through thehydrogen gas supply port and generated by plasma discharge is suppliedto the processing chamber while exhausted out through the exhaust port.

A seventeenth aspect is a manufacturing method of a semiconductordevice, including a step of generating mixed plasma by causing a mixedgas of hydrogen gas and oxygen or oxygen-containing gas supplied to aprocessing chamber to form a plasma discharge, and processing thestarting substrate by the mixed plasma; and a step of generatinghydrogen plasma by causing hydrogen gas supplied to the startingsubstrate to form a plasma discharge, and processing the substrate bythe hydrogen plasma.

An eighteenth aspect is the seventeenth aspect, wherein the step ofperforming a process with the hydrogen plasma is a first step, and astep of performing a process with the mixed plasma is performed as asecond step after the first step.

A nineteenth aspect is the seventeenth aspect, wherein a step ofperforming a process with the mixed plasma is a third step, and a stepof performing a process with the hydrogen plasma is performed as afourth step after the third step.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram of a plasma processing method ofEmbodiment 1;

FIG. 2 is an SEM photograph of the surface of the W substrate accordingto Embodiment 1 when subjected to the oxidation process, wherein (a) isan unprocessed surface, (b) is Comparative Example 1, (c) is ComparativeExample 2, and (d) is an Embodiment;

FIG. 3 is an explanatory diagram of a plasma processing method showingan example a gas flow and a discharge sequence in Embodiment 2;

FIG. 4 is an explanatory diagram showing conditions causing metalcontamination in which Embodiment 2 is applied;

FIG. 5 is an explanatory diagram showing conditions causing metalcontamination when the conventional example is applied;

FIG. 6 is a schematic longitudinal cross-sectional view of an MMT plasmasemiconductor manufacturing apparatus used in Embodiments 1 and 2; and

FIG. 7 is an explanatory diagram of the plasma processing method in theconventional example.

KEY

-   200 Wafer (substrate)-   234 Gas inlet port-   240 Shower plate-   224 Plasma production area

1. A substrate processing method comprising: generating mixed plasma byplasma discharge of a mixed gas of hydrogen gas and oxygen oroxygen-containing gas supplied to a processing chamber, and processing asubstrate on a surface of which a polysilicon film and a metal film areexposed by said mixed plasma; and generating hydrogen plasma by theplasma discharge of hydrogen gas supplied to the processing chamber, andprocessing said substrate by said hydrogen plasma, wherein theprocessing said substrate by said hydrogen plasma is a first step, andthe processing a substrate on a surface of which a polysilicon film anda metal film are exposed by said mixed plasma is a second step aftersaid first step.
 2. The substrate processing method of claim 1, whereinwhen a process of the substrate by the first step and the second step isrepeated, concentration of the oxygen gas remaining in the processingchamber in said first step, as a result of the preliminary substrateprocessing, is 11.1% or less.
 3. The substrate processing method ofclaim 1, wherein the oxygen gas or the oxygen-contained gas except forthe hydrogen gas is provided to the processing chamber in the firststep, and the flow ratio of oxygen gas in relation to said hydrogen gasin said first step is less than the flow ratio of oxygen gas in relationto said hydrogen gas in said second step.
 4. The substrate processingmethod of claim 1, wherein hydrogen gas is supplied in said first step,and the supply of said hydrogen gas is continued, and oxygen gas issupplied in addition to the hydrogen gas in said second step.
 5. Thesubstrate processing method of claim 1, wherein the oxygen gas or theoxygen-containing gas except for the hydrogen gas is provided to theprocessing chamber in the first step, and the flow rate of oxygen gascontained in the gas in said first step is less than the flow rate ofoxygen gas contained in said mixed gas in said second step.
 6. Thesubstrate processing method of claim 1, wherein oxygen gas is notsupplied in said first step.
 7. The substrate processing method of claim1, wherein the step of performing a process with said mixed plasma is athird step, and the step of performing a process with said hydrogenplasma is performed as a fourth step after said third step.
 8. Thesubstrate processing method of claim 7, wherein a concentration of theoxygen-containing gas remaining in the processing chamber in said fourthstep as a result of the plasma processing in the third step is 11.1% orless.
 9. The substrate processing method of claim 7, wherein thesubstrate is selectively oxidized by said mixed plasma in the thirdstep, and the supply of oxygen gas is stopped in said fourth step. 10.The substrate processing method of claim 7, wherein the oxygen gas orthe oxygen-containing gas except for the hydrogen gas is provided to theprocessing chamber in the first step, and a flow rate of oxygen gascontained in the gas in said fourth step is less than a flow rate ofoxygen gas contained in said mixed gas in said third step.
 11. Thesubstrate processing method of claim 7, wherein oxygen gas is notsupplied in said fourth step.
 12. A substrate processing methodcomprising: generating mixed plasma by plasma discharge of a mixed gasof hydrogen gas and oxygen or oxygen-containing gas supplied to aprocessing chamber, and processing a substrate on a surface of which apolysilicon film and a metal film are exposed by said mixed plasma; andgenerating hydrogen plasma by plasma discharge of hydrogen gas suppliedto the processing chamber, and processing said substrate by saidhydrogen plasma, wherein the processing a substrate on a surface ofwhich a polysilicon film and a metal film are exposed by said mixedplasma a is a third step, and the processing said substrate by saidhydrogen plasma is a fourth step after said third step; and the oxygengas or the oxygen-containing gas except for the hydrogen gas is providedto the processing chamber in the fourth step, and a flow ratio of oxygengas in relation to said hydrogen gas in the fourth step is less than aflow ratio of oxygen gas in relation to said mixed gas in said thirdstep.
 13. A substrate processing apparatus including: a processingchamber that processes a substrate on a surface of which a polysiliconfilm and a metal film are exposed; a mixed gas inlet port thatintroduces a mixed gas of hydrogen gas and oxygen or oxygen-containinggas into said processing chamber; a hydrogen gas inlet port thatintroduces hydrogen gas into said processing chamber; an exhaust portthat evacuates an interior of said processing chamber; a plasmagenerating part that: i) generates mixed plasma by plasma discharge ofsaid mixed gas of hydrogen gas and oxygen or oxygen-containing gassupplied to the processing chamber, and ii) generates a hydrogen plasmaby the plasma discharge of hydrogen gas supplied to the processingchamber; and a controller that performs control so that said mixed gasintroduced through said mixed gas inlet port is caused to form saidplasma discharge of said mixed gas of hydrogen gas and oxygen oroxygen-containing gas and is supplied to the substrate while exhaustedthrough said exhaust port, and so that said hydrogen gas introducedthrough said hydrogen gas inlet port is caused to form said plasmadischarge of hydrogen gas and is supplied to the substrate whileexhausted through said exhaust port; wherein the processing chamberprocesses said hydrogen plasma is a first step, and processes thesubstrate on a surface of which a polysilicon film and a metal film areexposed second step after said first step.
 14. The substrate processingapparatus of claim 13, wherein said controller performs control so thatsaid hydrogen gas introduced through said hydrogen gas inlet port iscaused to form a plasma discharge and supplied to the substrate whileexhausted through said exhaust port, and thereafter said mixed gasintroduced through said mixed gas inlet port is caused to form a plasmadischarge and supplied to the substrate while exhausted through saidexhaust port.
 15. The substrate processing apparatus of claim 13,wherein said controller performs control so that said mixed gasis causedto form a plasma discharge and supplied to the substrate while exhaustedthrough said exhaust port, and thereafter said hydrogen gasis caused toform a plasma discharge and supplied to the substrate while exhaustedthrough said exhaust port.